646981 has 2 divisors, whose sum is σ = 646982. Its totient is φ = 646980.

The previous prime is 646979. The next prime is 646991. The reversal of 646981 is 189646.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 401956 + 245025 = 634^2 + 495^2 .

It is a cyclic number.

It is not a de Polignac number, because 646981 - 2¹ = 646979 is a prime.

It is a super-2 number, since 2×646981² = 837168828722, which contains 22 as substring.

Together with 646979, it forms a pair of twin primes.

It is a nialpdrome in base 15.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (646991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323490 + 323491.

It is an arithmetic number, because the mean of its divisors is an integer number (323491).

2⁶⁴⁶⁹⁸¹ is an apocalyptic number.

It is an amenable number.

646981 is a deficient number, since it is larger than the sum of its proper divisors (1).

646981 is an equidigital number, since it uses as much as digits as its factorization.

646981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10368, while the sum is 34.

The square root of 646981 is about 804.3512914144. The cubic root of 646981 is about 86.4895907819.

The spelling of 646981 in words is "six hundred forty-six thousand, nine hundred eighty-one".